The invention broadly relates to control valves, and is specifically directed to an electrically controlled gas valve capable of modulating or on-off operation.
Gas valves are commonly used throughout the world to control fuel flow to a variety of gas burning appliances, such as furnaces and boilers. Due to the dangers inherent in natural gas and its use in residential, commercial and industrial applications, many safety requirements have been promulgated by various regulatory agencies. Not all requirements exist in all countries. Therefore, it is somewhat difficult to design and manufacture a valve suitable for global or international use.
One of the safety requirements that exists in some but not all countries is the capability to reliably regulate and/or shut off fuel flow to an appliance in high "back-pressure" situations. A straight forward solution to the problem is to provide a strong seal force, which may be produced by a spring or other biasing device.
The difficulty with this solution, particularly in a modulating valve, is that a commensurately large controlling force is required to open and control the valve. The problem is compounded somewhat by the fact that many gas valves, particularly for residential use, are controlled by an electric signal. With a modest electrical current, it is difficult to generate a force that not only is capable of overcoming a strong biasing force, but is also capable of effecting accurate flow control.
The inventive gas valve overcomes these problems in a unique manner by utilizing an electrically conductive winding that functions as a speaker coil to generate a magnetomotive force that can be used either to modulate the main flow valve or to operate it in an on-off manner.
The force generated by the voice coil is not used directly to oppose the spring biasing force that maintains the main flow valve in a closed position. Rather, it is used to operate a smaller control valve that in turn determines the pressure acting against a diaphragm that controls the main control valve.
In the preferred embodiment, two small control valves, one normally closed and one normally open, act in concert over a range of movement in response to the thermostatically controlled electric current signal to position the main control valve as a function of demand. The valve operates uniquely to provide a maximum flow of gas when the electric current signal reaches a threshold level, and to thereafter reduce the output gas flow linearly as a function of the increasing electric current signal.
The modulating operation of the main flow valve may be easily changed by eliminating a mechanical linkage between the two control valves, which changes the main flow valve to on-off operation mode that is common in many residential appliances, such as furnaces.
The inventive valve is small, compact and relatively simple, while at the same time satisfying the various safety requirements of most countries, thus permitting global use.